
%0 Journal Article
%A Smith, DW 
%T Electronegativity Equilibration and the Methylene Increment in Organic Thermochemistry
%J Australian Journal of Chemistry
%D 1995/01/01
%V 48
%N 1
%P 65-77
%K 
%R https://doi.org/10.1071/CH9950065
%U https://www.publish.csiro.au/paper/CH9950065 
%X It is proposed that the magnitude of the ' methylene increment' &#8710;&#8710; fH&#176;(CnH2n+1X, Cn+1H2n+3X) between the heats of formation of successive members of a homologous series can be rationalized by considering the variation of carbon-carbon bond enthalpies Eij. These are deemed to be related to the products qiqj of the fractional charges on adjacent carbon atoms by the relation: Eij=E&#176;-aqiqj where E&#176; and a are empirical constants, and the fractional charges are estimated by electronegativity equilibration. For the homologous series CnH2n+1X (X = H, Cl , Br, I, OH, OMe , NH2), a linear correlation is found between the mean increment [&#8710;&#8710; fH &#176;(CH3X, CnH2n+1)]/(n-1) and the mean charge product &#8721;qiqj/(n - 1). The empirically obtained value for E&#176; is in close agreement with the experimental C-C bond enthalpy in diamond. For all series, the calculated methylene increment converges to a common value of 20.6 kJ mol-1. The treatment may provide an attractive alternative to existing methods for the estimation of the heats of formation of organic compounds, requiring fewer empirical parameters. 
